Netnewswire is used to view (read) RSS feeds.
iPhoto photocasts can be viewed by others with iPhoto or any RSS Reader.
Photocasts via iPhoto require that you are a .mac user to host them.
One way to make an RSS feed of photos is to simply use Flickr. When you post photos there, you automatically have RSS feeds available to you.
For instance, here is the feed for the photos/images I have on Flickr:
OwlBoy's Photos
-Owl